The common thread is that most of the presenters & audience know at least one dialect of lisp (eg Common Lisp, Scheme, Clojure, Emacs Lisp, etc). But it is definitely a polyglot (not just lisp-related) group & presentations on non lisp-related subjects are encouraged

The format is usually "educational lightning talks" (background + 5 minute presentation + 5 minutes for QA), with all attendees invited to present if they feel like it. Followed by free beer.